Will this latest fix solve Boise ponds’ E. coli problem?

Doug Holloway wouldn’t speculate Monday on when he expects to reopen the ponds at Esther Simplot Park for swimming and other recreation.

Holloway, Boise’s Parks and Recreation director, did say that decision could come soon, because E. coli levels have been low and falling for the past five days or so.

“If the trend continues the way it’s going, we believe that we can huddle those that we can get together with and pick a date to get it open,” Holloway said.

Holloway closed both ponds in Esther Simplot Park and Quinn’s Pond, just south of the park, on June 21 after tests showed elevated E. coli levels in all three bodies of water. Lab analysis showed goose and dog poop were the main sources of the E. coli.

Never miss a local story.

Sign up today for unlimited digital access to our website, apps, the digital newspaper and more.

Nine days after closing Quinn’s Pond, Holloway re-opened it, as tests showed declining E. coli levels there. But the E. coli in Esther Simplot Park has been more persistent.

A stormwater detention basin east of the park is one factor, said Kate Harris, the city of Boise’s interim water quality manager. The basin, north of Idaho River Sports and west of Whitewater Park Boulevard, is meant to collect and drain stormwater, Holloway said.

But its drainage function wasn’t working correctly. Stagnant water was accumulating in the pond. Later, the city discovered some of that water was seeping through its western bank into the east side of a pond in Esther Simplot Park, Harris said.

Bright green algae was growing on the sand where the seepage was arriving in the pond, she said. Tests of that water showed extremely high levels of E. coli, Harris said. Boise drained the detention basin last week, she said, and E. coli levels in Esther Simplot Park have declined since.

Harris said the detention basin wasn’t the only source of E. coli in the park.

Holloway said the city and the Ada County Highway District, which uses the basin to capture runoff from Whitewater Park Boulevard, are working to fix the drainage and filtration system. The highway district built the basin, and the city expanded it, district spokeswoman Nicole Du Bois said in an email Tuesday. The district plans to conduct exploratory excavation Wednesday to determine why the basin is not draining properly, Du Bois said.